It is well known that the fatigue life of a stressed work piece with a hole therethrough can be significantly increased by coldworking the hole. Several techniques have been developed to coldwork the hole to increase the fatigue life.
One such technique is disclosed in U.S. Pat. No. 3,566,662 which uses an axial or helical pre-split tubular member through which an expansion mandrel is passed to expand the tubular member radially into the surface of the work piece at the hole and expand the hole beyond its elastic limit. While this technique does offer the advantage of being able to remove the tubular member after the hole has been coldworked, it offers the disadvantage that one area of the hole will be coldworked to a lesser extent where the split in the tubular member is located.
It has subsequently been found, however, that a hole may be coldworked by passing an expansion mandrel through a seamless tubular member. This has the advantage of uniformly coldworking the work piece about the hole but the disadvantage that once the tubular member has been expanded into place, it is locked into the hole of the work piece so that it cannot be easily removed.